Normally in a shuttleless loom particularly in a jet loom, a weft length measuring device is provided to preliminarily measure a necessary length of the weft needed for one weft inserting operation and store the weft. As for such kind of weft length measuring device, conventionally available in the prior art was a so-called pipe type weft length measuring device in which the weft was stored in a storage pipe while being floated in airflow. In this pipe type weft length measuring device, however, the weft is subjected to relatively large resistance when it is drawn out from the storage pipe by the airflow upon the weft inserting. Furthermore, the weft is inserted in the storage pipe also by the airflow. Consequently, it was difficult to store an exact length of weft needed for one insertion. As a result, the weft inserting operation became unstable and improper-insertion often occurred, which was deemed a drawback of the prior system. In order to obviate the drawbacks of said pipe type weft length measuring device, a new drum type weft length measuring device is proposed in which a weft supplied from a weft supply bobbin is continuously wound up on the tapered surface of a weft storage drum, in a coiled form and the thus wound weft is drawn out upon the weft inserting. On this weft length measuring device, equipped is a pair of weft engaging pins, which control the wound amount of the weft and its out-feeding, in a retractable manner relating to the tapered periphery of the weft storage drum.
Said weft engaging pins mounted on the drum type weft length measuring device of the prior art have a structure such that the pins can turnably move around a plane perpendicular to the axial line of the drum. Therefore, when a weft is coiled on the tapered surface of the drum, the first turn of the weft is engaged status until very instant when said weft engaging pin disappears in the drum. Accordingly, the second and later turns of the weft tend to run over the first turn and to move toward the drawing-out direction. In consequence, there is a disadvantage that the weft is often entangled disturbing the weft inserting operation. On the drum, on the other hand, there are long holes extending in the peripheral direction of the drum, to permit said weft engaging pins to appear on and disappear in the drum. The first turn of the weft located close to the long holes lies more towards the inner side of the drum than the weft of the second and turns on the drum. Therefore, at an instant when said weft engaging pin is retracted in the drum, the second and later turns of the weft are apt to run over the weft of the first turn. It easily causes entanglement of the weft which is troublesome to the weft inserting operation.
Also, in the drum type weft length measuring device of the prior art as described above, a pair of weft engaging pins are mounted in the axial direction of the drum in an alternately retractable manner relating to the drum periphery of the weft storage drum. Out of these weft engaging pins, one pin mounted on the weft winding tube is protruded when a necessary length of the weft is wound on the drum for one insertion, while working to separate securely the weft readily wound from the weft to be newly wound. The other pin located on the drawing-out side, works to restrict, when one pin disappears in the drum during winding a necessary length of the weft for one insertion, the weft wound so far to move toward the drawing-out side, thus ensuring a completion of winding another necessary length of the weft for the next insertion. Consequently, said one pin shall be protruded and retracted on a position allowing secure separation of the weft. In addition, it is also another important factor to keep a suitable spacing between the positions of both pins. In other words, in order that one pin can securely separate the weft, the other pin should be distantly mounted because the weft wound on the drum can move in a larger distance. On the other hand, however, if the other pin is located too far from one pin while permitting the wound weft to move by a long distance, the weft may be slackened causing possibly entanglement and a trouble in the weft inserting function. As described above, the spacing of retract positions of two weft engaging pins become a very important matter.
However, according to the method of the prior art, weft engaging pins take fixed distance therebetween once they are set to engage the weft. Therefore, it was a disadvantage of the prior system that the foregoing problem was not satisfactorily solved.